Numerical study on the lobed nozzles for enhancing the mixing and combustion performance of rocket-based combined cycle engine

a b s t r a c tA rocket-based combined-cycle (RBCC) engine has become one of the most efficient propulsion systems for future reusable space transportation vehicles.The degree of mixing impacts the combustion performance of the RBCC engine.Lobed mixer is a widely investigated in RBCC engine but lobed nozzle especially under a high temperature environment has yet to be comprehensively explored.In this study, the mixing and combustion performance of the RBCC engine are investigated with different lobed nozzles and with different arrangements of the flame holder, using the three-dimensional numerical simulation.The numerical method is validated by comparing it with the experimental data.The mixing performance, the vortex structure, the total pressure recovery, and the combustion efficiency of the RBCC engine are studied.The results reveal that the lobed nozzle enhances the mixing and combustion performance.It is found that the thermal mixing efficiency of the lobed nozzle is 56% higher and the velocity mixing coefficient of the lobed nozzle is 7% lower than the prototype circular nozzle.The lobed nozzle improves the combustion efficiency approximately by 6.1%.The combustion in the RBCC engine combustor can improve the velocity mixing performance by nearly 30% compared with cold flow.The results show that the nozzle with the lobed structure leads to the formation of high-intensity streamwise vortices.The flame holder forms a high-velocity region which affects the primary flow penetration depth generated by the lobe nozzle.To improve the mixing performance, the flame holder and the lobe tip have to be matched correctly.